Chrysler 48RE Transmission

48RE Transmission Specs & Ratios

The 48RE four speed automatic transmission represents an evolution of the previous 47RE model and can be found mated to the Cummins Turbodiesel in Ram pickups from 2003 to 2007 model years. The transmission features a strength designation of "8" on a scale from 1 to 9. The 48RE is both heavier and stronger than the 47RE, although the two transmissions share identical ratios. Although the 48RE is considered a significant improvement over its predecessor, it quickly became dated as power ratings for the Cummins Turbodiesel surged to over 600 lb-ft by 2007, the last model year of the 5.9L Cummins ISB. Chrysler would ultimately replace the 48RE with its first diesel specific transmission platform, the 68RFE, following the introduction of the 6.7L Cummins.

Chrysler's strength designation of the 48RE is an "8" on a scale of 1 to 9, although this designation is arbitrary and meaningless unless comparing the relative strength between two or more Chrysler drivetrain products. The 48RE automatic transmission features an actual input torque rating between 560 and 570 lb-ft of torque. Meanwhile, the standard Cummins Turbodiesel peaked at 610 lb-ft by the 2005 model year. As a result, the 5.9L Cummins was designed to detune itself when necessary to promote transmission longevity. The engine will produce its peak 610 lb-ft torque, but only in instances when accessory load brings the actual engine torque output (at the crankshaft) into the 570 lb-ft range. In all other cases, the engine will detune to roughly 570 lb-ft under full load. The limits of the transmission are quickly realized in the presence of performance enhancing modifications such as electronic tuning devices.

The transmission features a "Tow/Haul" setting that is activated via a shifter mounted switch. The 48RE's Tow/Haul function is not necessarily a "smart" function such as those found on modern engine/transmission combinations with integrated exhaust brake technology and vehicle speed management systems. When the Tow/Haul setting is activated, torque converter lockup is engaged and the transmission shift schedule eliminates overdrive (4th gear) upshifts, thus direct drive (3rd gear) becomes the final available drive gear. Towing significant weight in overdrive is not recommended, as drive wheel torque is reduced and the load placed on the transmission can contribute to reduced longevity.

The 48RE is designed to run at a transmission fluid temperature at or near 200° F, although temperature spikes well beyond this are common while towing, especially in overdrive where transmission load is high. If transmission fluid temperature exceeds 260° F the PCM will engage the torque converter clutch and force a 4th to 3rd downshift in order to reduce the load through the transmission. When this occurs, the transmission will not command a 4th gear shift until the fluid temperature has been reduced to 230° F. Additionally, the PCM will prevent torque converter clutch lockup and 3rd to 4th upshifts when the transmission fluid temperature is below 50° F in order to reduce engine and transmission warm up time. A deep dish transmission pan and heavy duty transmission cooler are somewhat common upgrades for 48RE owners in order to keep transmission fluid temperatures reasonable while towing - reoccurring excessive transmission fluid temperature can greatly diminish transmission life.

The 48RE features four shift schedules, technically known as governor pressure curves. Governor pressure is electronically controlled relative to engine speed and is used to command upshifts and downshifts according to engine speed and load. The four schedules are as follows:

Transmission fluid temperature at or below 30° F - Shifts are delayed and the engine is allowed to rev higher to help the engine and transmission reach normal operating temperature in less time. Shifts are typically harsh while this schedule is in effect.

Transmission fluid temperature at or above 50° F - The transmission's normal adaptive shift strategy is in effect. The adaptive strategy is a dynamic shift schedule that commands upshifts and downshifts based on various operating conditions, including engine speed and load.

Wide open throttle (WOT) - At WOT, upshifts are originally commanded by the PCM at predetermined optimal engine speeds. The PCM perpetually learns and creates an optimal WOT upshift schedule based on the time required to complete a shift at a given engine speed/load compared to the desired preprogrammed values. The WOT shift schedule is therefore adjusted routinely based on the outcome of transmission shift events.

Transfer case 4 wheel drive low engaged - In order to compensate for inherent accelerator pedal sensitivity in low range (resulting from significantly higher engine torque multiplication through the drivetrain) the PCM will command upshifts much sooner when the transfer case is placed in low range.